Atta-ur Rahman, Shakeel Mahmood, Mohammad Dawood, Ghani Rahman, and Fang Chen
This chapter analyzes the impacts of climate change on flood factors and extent of associated damages in the Hindu Kush (HK) region. HK mountains system is located in the west of the Himalayas and Karakorum. It is the greatest watershed of the River Kabul, River Chitral, River Panjkora, and River Swat in the eastern Hindu Kush and River Amu in western Hindu Kush. The Hindu Kush system hosts numerous glaciers, snow-clad mountains, and fertile river valleys; it also supports large populations and provides year-round water to recharge streams and rivers. The study region is vulnerable to a wide range of hazards including floods, earthquakes, landslides, desertification, and drought. Flash floods and riverine floods are the deadliest extreme hydro-meteorological events. The upper reaches experience characteristics of flash flooding, whereas the lower reach is where river floods occur. Flash floods are more destructive and sudden. Almost every year in summer, monsoonal rainfall and high temperature join hands with heavy melting of glaciers and snow accelerating discharge in the river system. In the face of climate change, a significant correlation between rainfall patterns, trends in temperature, and resultant peaks in river discharge have been recorded. A rising trend was found in temperature, which leads to early and rapid melting of glaciers and snow in the headwater region. The analysis reveals that during the past three decades, radical changes in the behavior of numerous valley glaciers have been noted. In addition, the spatial and temporal scales of violent weather events have been growing, since the 1980s. Such changes in water regimes including the frequent but substantial increase in heavy precipitation events and rapid melting of snow in the headwater region, siltation in active channels, excessive deforestation, and human encroachments onto the active flood channel have further escalated the flooding events. The HK region is beyond the reach of existing weather RADAR network, and hence forecasting and early warning is ineffective. Here, almost every year, the floods cause damages to infrastructure, scarce farmland, and sources of livelihood.
Parvin Sultana and Paul Thompson
Floodplains are ecologically diverse and important sources of livelihood for rural people. Bangladesh is one of the most floodplain-dominated countries and supports the highest density of rural population in the world. The experience of Bangladesh in floodplain management efforts provides evidence, lessons, and insights on a range of debates and advances in the management of floodplain natural resources, the challenges of climate change, and the role of local communities in sustaining these resources and thereby their livelihoods. Although floodplain areas are primarily used for agriculture, the significance and value of wild common natural resources—mainly fish and aquatic plants—as sources of income and nutrition for floodplain inhabitants has been underrecognized in the past, particularly with respect to poorer households. For example, capture fisheries—a common resource—have been adversely impacted by the building of embankments and sluice gates and by the conversion of floodplains into aquaculture farms, which also exclude poor subsistence users from wetland resources. More generally, an overreliance on engineering “solutions” to flooding that focused on enabling more secure rice cultivation was criticized, particularly in the early 1990s during the Flood Action Plan, for being top down and for ignoring some of the most vulnerable people who live on islands in the braided main rivers. Coastal embankments have also been found to have longer term environmental impacts that undermine their performance because they constrain rivers, which silt up outside these polders, contributing, along with land shrinkage, to drainage congestion. Locals responded in an innovative way by breaking embankments to allow flood water and silt deposition in to regain relative land levels.
Since the early 1990s Bangladesh has adopted a more participatory approach to floodplain management, piloting and then expanding new approaches; these have provided lessons that can be more general applied within Asia and beyond. Participatory planning for water and natural resource management has also been adopted at the local level. Good practices have been developed to ensure that disadvantaged, poor stakeholders can articulate their views and find consensus with other local stakeholders. The management of smaller water-control projects (up to 1,000 ha) has been taken on by community organizations, and in larger water-control projects, there is collaborative management (also called “co-management”) among a hierarchy of groups and associations and the appropriate government agency. In fishery and wetland management, many areas have been managed by community organizations to sustainably restore common resources, although their rights to do this were lost in some cases. Associated with community management are successful experiments in adopting a more system-based approach, called “integrated floodplain management,” which balances the needs of agriculture and common natural resources, for example, by adopting crops with lower water demands that are resilient to less predictable rainfall and drier winters, and enable communities to preserve surface water for wild aquatic resources. Bangladesh also has had success in demonstrating the benefits of systematic learning among networks of community organizations, which enhances innovation and adaptation to the ever-changing environmental challenges in floodplains.
Marian Muste and Ton Hoitink
With a continuous global increase in flood frequency and intensity, there is an immediate need for new science-based solutions for flood mitigation, resilience, and adaptation that can be quickly deployed in any flood-prone area. An integral part of these solutions is the availability of river discharge measurements delivered in real time with high spatiotemporal density and over large-scale areas. Stream stages and the associated discharges are the most perceivable variables of the water cycle and the ones that eventually determine the levels of hazard during floods. Consequently, the availability of discharge records (a.k.a. streamflows) is paramount for flood-risk management because they provide actionable information for organizing the activities before, during, and after floods, and they supply the data for planning and designing floodplain infrastructure. Moreover, the discharge records represent the ground-truth data for developing and continuously improving the accuracy of the hydrologic models used for forecasting streamflows. Acquiring discharge data for streams is critically important not only for flood forecasting and monitoring but also for many other practical uses, such as monitoring water abstractions for supporting decisions in various socioeconomic activities (from agriculture to industry, transportation, and recreation) and for ensuring healthy ecological flows. All these activities require knowledge of past, current, and future flows in rivers and streams.
Given its importance, an ability to measure the flow in channels has preoccupied water users for millennia. Starting with the simplest volumetric methods to estimate flows, the measurement of discharge has evolved through continued innovation to sophisticated methods so that today we can continuously acquire and communicate the data in real time. There is no essential difference between the instruments and methods used to acquire streamflow data during normal conditions versus during floods. The measurements during floods are, however, complex, hazardous, and of limited accuracy compared with those acquired during normal flows. The essential differences in the configuration and operation of the instruments and methods for discharge estimation stem from the type of measurements they acquire—that is, discrete and autonomous measurements (i.e., measurements that can be taken any time any place) and those acquired continuously (i.e., estimates based on indirect methods developed for fixed locations). Regardless of the measurement situation and approach, the main concern of the data providers for flooding (as well as for other areas of water resource management) is the timely delivery of accurate discharge data at flood-prone locations across river basins.